Composition, structure, and thermal expansion of Ca3Fe 4S3O6 and CaFeSO

Article abstract of DOI:10.1023/B:INMA.0000037931.30753.56

The iron calcium oxysulfides Ca₃Fe₄S ₃O₆ and CaFeSO are synthesized by reacting mixtures of CaO and FeS in an inert atmosphere. Their elemental compositions and lattice parameters are determined by x-ray microan

Full text of DOI:10.1023/B:INMA.0000037931.30753.56

Inorganic Materials, Vol. 40, No. 8, 2004, pp. 845–850. Translated from Neorganicheskie Materialy, Vol. 40, No. 8, 2004, pp. 969–974.
Original Russian Text Copyright © 2004 by Selivanov, Chumarev, Gulyaeva, Mar’evich, Vershinin, Pankratov, Korepanova.
Composition, Structure, and Thermal Expansion
of Ca3Fe4S3O6 and CaFeSO
E. N. Selivanov, V. M. Chumarev, R. I. Gulyaeva, V. P. Mar’evich,
A. D. Vershinin, A. A. Pankratov, and E. S. Korepanova
Institute of Metallurgy, Ural Division, Russian Academy of Sciences,
ul. Amundsena 101, Yekaterinburg, 620016 Russia
e-mail: pcmlab@sky.ru
Received October 22, 2003
Abstract—The iron calcium oxysulfides Ca3Fe4S3O6 and CaFeSO are synthesized by reacting mixtures of
CaO and FeS in an inert atmosphere. Their elemental compositions and lattice parameters are determined by x-
ray microanalysis and x-ray diffraction. From the temperature-dependent lattice parameters of the oxysulfides
(measured up to 1020 K), their thermal expansion coefficients are evaluated.
INTRODUCTION
tances [10, 11]. These distances are determined by the
O–S–O and S–S bond lengths along the a and c axes,
respectively. Detailed structural data for other iron cal-
cium oxysulfides are missing, and their thermal proper-
ties have not been studied.
The purpose of this work was to refine the composi-
tion and structure of the iron calcium oxysulfides in
question, to determine their lattice parameters, and to
investigate their thermal properties in an inert atmo-
sphere.
The formation of iron calcium oxysulfides, belong-
ing to a poorly explored class of inorganic compounds,
was observed earlier in the production of ferrous and
nonferrous metals [1–6]. The available data on the com-
position and structure of these compounds are contra-
dictory. Based on x-ray diffraction (XRD) data, the
compositions of two iron calcium oxysulfides were
determined as Ca3Fe4S3O4 or Ca3Fe4S3O6 (OS-1) and
CaFeSO or Ca2Fe2S2O3 (OS-2) [7]. According to Yary-
gin et al. [4, 8], the composition of OS-1 is Ca3Fe4S3O6,
whereas Schuermann and Fischer [9] believe that the
composition of this compound is close to Ca3Fe4S3O4.
The results reported in [10, 11] indicate that, at temper-
atures from 1070 to 1270 K and an oxygen partial pres-
EXPERIMENTAL
XRD measurements were made at temperatures of
up to 1020 K on a DRON-2.0 powder diffractometer
(CoKα radiation, pyrolytic graphite diffracted-beam
monochromator, silicon internal standard) equipped
with a UVD-2000 high-temperature attachment, which
enabled studies in a helium atmosphere. Lattice param-
eters were determined by standard techniques [13, 14].
sure pO = 10–25 Pa, the composition of OS-1 is
Ca3Fe4S3O4, and that of OS-2 is CaFeSO. At the same
time, Schuermann and Fischer [9] hold that OS-2 has
the Ca2Fe2S2O3 stoichiometry. According to the x-ray
2
microanalysis data reported by Koch et al. [12], the The temperature was measured by a Pt/Pt–10% Rh
composition of OS-1 is Fe 40.5, Ca 23.0, S 16.0, and O thermocouple with an accuracy of 0.7%. The elemen-
20.5 wt %, and that of OS-2 is Fe 39.0, Ca 26.5, S 25.0, tal composition of the synthesized phases was deter-
and O 9.5 wt %.
mined on a CAMEBAX x-ray microanalyzer.
The XRD pattern of CaFeSO was indexed, by anal-
Iron calcium oxysulfides were synthesized by heat-
ogy with CaZnSO, in hexagonal symmetry with lat- ing appropriate starting mixtures in evacuated tubes or
tice parameters a = 0.632 nm and c = 0.368 nm, as under flowing helium in a silica reactor mounted in a
inferred from the smallest possible cation–cation dis- tube furnace (Table 1). The starting iron monosulfide
Table 1. Synthesis conditions for iron calcium oxysulfides
Mixture composition, wt %
Sample no.
T, K
τ, min
Atmosphere
CaO
FeS
Fe
1
2
38.95
32.62
61.05
51.14
–
1220
1190
20
Vacuum (10–2 Pa) in a tube
Flowing helium (0.1 MPa)
16.24
240
0020-1685/04/4008-0845 © 2004 MAIK “Nauka/Interperiodica”

846
SELIVANOV et al.
in particle size) in the molar ratio 1.0 : 1.0 was pressed
into pellets, which were then placed in corundum cru-
cibles and fired in evacuated tubes at 1220 K for 20 min
(sample 1). Oxysulfide OS-2 was prepared from a mix-
ture of calcium oxide, iron sulfide, and metallic iron
powders in the molar ratio 1.0 : 1.0 : 0.5, which were
pressed into pellets and fired at 1190 K for 4 h in flow-
ing helium (100 ml/min) (sample 2). Fe metal was
introduced into the reaction system in order to drive the
reaction
1
2
3
4
200 µm
(a)
3FeO
Fe + Fe2O3
(1)
to the left and to bind excess CaS.
5
6
RESULTS AND DISCUSSION
2
5
7
The x-ray microanalysis data for samples 1 and 2
(Table 2, Fig. 1) indicate that phase-pure iron calcium
oxysulfides are rather difficult to obtain. Sample 1 con-
tained, along with OS-1, a significant amount (about
20%) of calcium sulfide and a small amount of calcium
oxide. In addition, the sample contained Fe metal parti-
cles (2–5 wt %), which probably resulted from FeO
decomposition into Fe2O3 and Fe during cooling.
According to x-ray microanalysis results, the composi-
tion of OS-1 was ꢀCa3Fe4S3O6. At the same time, the
present and earlier results [4, 8, 9] do not rule out the
200 µm
(b)
Fig. 1. X-ray scan images of samples (a) 1 and (b) 2;
(1−7) see Table 2.
was prepared by slowly heating a mixture of carbonyl
iron and extrapure-grade sulfur to 1270 K in evacuated
(10–2 Pa) silica tubes, followed by holding for 50 h. The possibility that this compound has a variable oxygen
purity of the reaction product was checked by XRD and stoichiometry.
chemical analysis. Calcium oxide (pure grade) was pre-
The major phase in sample 2 was OS-2, as deter-
calcined at 1270 K.
mined by x-ray microanalysis. Its composition was Ca
To prepare compound OS-1, a mixture of calcium 27.52, Fe 38.57, S 21.98, and O 12.12 wt %, which cor-
oxide and iron monosulfide powders (less than 0.1 mm responds to the stoichiometry CaFeSO. Sample 2 also
Table 2. X-ray microanalysis data for iron calcium oxysulfides
No.
Weight percent
Atomic percent
Phase
CaO
sample
1
phase*
Ca
Fe
S
O**
Ca
Fe
S
O**
1
2
3
4
2
5
6
5
7
71.5
0.6
1.4
98.7
42.6
0.8
1.0
0.9
28.5
–
49.9
0.1
97.7
26.6
0.5
0.1
49.9
–
0.77
1.53
Fe
23.5
55.2
0.1
19.0
43.7
14.9
0.2
–
20.4
49.8
20.6
49.4
0.01
32.4
0.3
–
Ca3Fe4S3O6
CaS
2
97.8
68.9
38.6
68.8
64.4
0.01
0.01
99.8
41.8
24.4
41.2
44.4
Fe
3.7
2.6
22.0
2.1
24.7
12.1
25.9
–
3.2
24.4
2.6
2.7
24.3
2.2
52.3
26.9
54.0
–
FeO
27.5
3.2
CaFeSO
FeO
3.6
32.0
4.0
51.5
FeS
* See Fig. 1.
** Determined as the balance.
INORGANIC MATERIALS Vol. 40 No. 8 2004

COMPOSITION, STRUCTURE, AND THERMAL EXPANSION
Table 3. Indexing scheme for Ca3Fe4S3O6
847
h
k
l
2θobs, deg
2θcalc, deg
∆(2θ), deg
dobs, nm
Iobs, %
0
2
2
2
2
0
4
2
4
4
2
4
5
4
6
4
6
2
4
4
2
6
2
0
0
2
2
0
0
0
0
1
2
2
0
1
4
2
2
0
0
0
0
2
4
2
2
2
0
1
3
4
0
4
3
3
5
4
2
0
0
5
3
7
6
6
7
3
8
23.59
35.63
37.36
39.39
44.88
48.09
53.99
55.77
68.08
72.65
74.31
75.32
75.69
79.90
91.65
92.13
96.58
97.31
99.36
99.50
103.31
121.78
122.80
23.58
35.57
37.45
39.37
44.85
48.25
54.00
55.75
68.03
72.73
74.23
75.30
75.72
79.88
91.74
92.14
96.62
97.26
99.44
99.44
103.26
121.83
122.87
–0.01
+0.06
–0.09
+0.02
+0.03
–0.17
–0.01
+0.02
+0.05
–0.08
+0.08
+0.02
–0.03
+0.02
–0.08
–0.01
–0.04
+0.08
–0.08
+0.06
+0.05
–0.05
–0.07
0.4381
0.2926
0.2795
0.2656
0.2345
0.2197
0.1972
0.1914
0.1599
0.1511
0.1482
0.1465
0.1459
0.1394
0.1248
0.1243
0.1199
0.1192
0.1174
0.11728
0.11413
0.10245
0.10195
37
10
13
11
100
78
19
6
7
16
5
8
17
5
1
1
3
6
5
5
3
2
7
Table 4. Indexing scheme for CaFeSO
h
k
l
2θobs, deg
2θcalc, deg
∆(2θ), deg
dobs, nm
Iobs, %
0
1
1
0
1
1
1
0
1
1
1
2
2
2
2
0
0
0
0
0
0
0
0
1
0
1
0
0
1
1
2
0
1
4
2
3
4
6
0
8
4
3
6
3
6
18.11
31.90
33.27
36.69
36.97
42.53
49.40
56.47
56.90
66.20
69.77
73.50
92.80
99.82
120.50
18.12
31.94
33.25
36.71
36.96
42.52
49.44
56.38
56.91
66.28
69.82
73.56
92.87
99.85
120.39
–0.01
–0.03
+0.02
–0.02
+0.01
+0.01
+0.04
+0.09
–0.01
–0.07
–0.05
–0.06
–0.16
–0.03
+0.11
0.5687
0.3257
0.3127
0.2844
0.2823
0.2468
0.2142
0.1892
0.1879
0.1639
0.1565
0.1496
0.1236
0.1170
0.1031
25
19
38
69
100
74
16
9
40
39
23
9
9
8
8
INORGANIC MATERIALS Vol. 40 No. 8 2004

848
SELIVANOV et al.
a, nm
a, nm
0.379
0.795
0.791
0.787
c, nm
0.377
0.375
c, nm
1.147
0.90
0.89
0.88
1.143
1.139
0.87
1.135
V, nm3
V, nm3
0.142
0.141
0.140
0.57
0.56
0.55
0.54
250
0.139
1050
450
650
850
0.138
250
T, K
450
650
850 T, K
Fig. 3. Temperature dependences of lattice parameters for
CaFeSO.
Fig. 2. Temperature dependences of lattice parameters for
Ca Fe S O .
3
4 3 6
contained Fe metal and trace levels of FeO, FeS, and has a hexagonal cell with a = 0.37571(8) nm, c =
1.13691(43) nm, and V = 0.1390(1) nm3. These values
differ somewhat from the data reported by Jha et al. [10]
and Igiehon et al. [11]. The x-ray density of OS-2, ρx =
CaS (Table 2).
The XRD data for Ca3Fe4S3O6 could be indexed in
the tetragonal system (Table 3), with lattice parameters
a = 0.7889(1) nm and c = 0.8741(1) nm (V =
0.5440(1) nm3). The main diffraction peaks agreed well
with earlier results [8, 9]. The x-ray density of this
oxysulfide, ρx = 3.32 g/cm3, is consistent with the den-
sity of sample 1 determined by theArchimedes method,
ρmeas = 3.51 g/cm3, given that the sample contained
impurity phases.
The XRD pattern of CaFeSO (Table 4) is close to
that given in the ICDD Powder Diffraction File for
Ca2Fe4S3O4 (card 43-0600) [7]. In contrast to earlier
studies [10, 11], we observed a splitting of the reflec-
tion with d = 0.283 nm into two components with d
spacings of 0.2844 and 0.2823 nm and revealed a line
with d = 0.2142 nm. Detailed analysis of XRD data sug-
3.45 g/cm3, is substantially lower than the measured
density of sample 2, ρmeas = 3.85 g/cm3, which is asso-
ciated with the presence of impurity phases, in particu-
lar, Fe metal.
Measurements of lattice parameters as functions of
temperature for Ca3Fe4S3O6 in helium (Fig. 2) demon-
strate that a remains almost constant up to 600 K and
slightly increases above this temperature. At the same
time, the c parameter and unit-cell volume of OS-2
increase rapidly over the entire temperature range stud-
ied. The anisotropic thermal expansion of the crystal
lattice influences the c/a ratio, which can be accounted
for in terms of chemical deformation related to compo-
gests that CaFeSO is isostructural with CaZnSO [15] and sitional changes during heating.
INORGANIC MATERIALS Vol. 40 No. 8 2004

COMPOSITION, STRUCTURE, AND THERMAL EXPANSION
849
Table 5. Coefficients in the best fit equations for the temperature-dependent lattice parameters of iron calcium oxysulfides
Compound
Ca3Fe4S3O6
Lattice parameters
K0
K1 × 105
K2 × 108
R2, %
a, nm
c, nm
V, nm3
a, nm
c, nm
V, nm3
0.79313
0.87693
0.55193
0.37414
0.37647
0.13926
–2.07336
–2.11735
–4.32335
0.49358
2.41108
4.39143
6.20648
0
97.5
99.8
99.3
97.8
98.3
99.2
CaFeSO
–0.77639
–0.52873
2.08908
1.64538
In the case of CaFeSO, c also rises with temperature
more rapidly than a (Fig. 3). In contrast to that of OS-1,
the a parameter of CaFeSO increases steadily, starting
at room temperature.
The temperature-dependent lattice parameters of the
two oxysulfides can be represented by polynomials of
the form
P = K0 + K1T + K2T2,
(2)
where P = a (nm), c (nm), or V (nm3), and K0, K1, and
K2 are regression coefficients (Table 5).
α × 105, K–1
8
6
4
2
OS-1
The thermal expansion coefficients (α) of the
αc
oxysulfides were evaluated as [14]
α = 1/P(dP/dT).
(3)
The results (Fig. 4) demonstrate that the αa of
Ca3Fe4S3O6 is close to zero up to ꢀ600 K and passes
through a maximum at about 800 K. At the same time,
the αc of this oxysulfide rises almost linearly, from
1.0 × 10–5 to 8.0 × 10–5 K–1, with increasing tempera-
ture. The thermal expansion coefficients of OS-2 are,
on the whole, smaller than those of OS-1, but the αc and
αa versus temperature curves for OS-2 are similar in
shape for those for OS-1.
αa
CONCLUSIONS
0
The compositions of the iron calcium oxysulfides
obtained in this work are Ca3Fe4S3O6 and CaFeSO.
According to XRD results, Ca3Fe4S3O6 has a tetragonal
structure, and CaFeSO has a hexagonal structure. It
seems likely that both Ca3Fe4S3O6 and CaFeSO have
variable oxygen stoichiometries. The thermal expan-
sion of these oxysulfides is anisotropic: c increases with
temperature more rapidly than a.
OS-2
αc
1.5
1.0
0.5
0
αa
ACKNOWLEDGMENTS
This work was supported by the Russian Foundation
for Basic Research, grant R2002 Ural 02-03-96448.
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